The proposed research addresses a mission statement set forth by the NIH in regards to the need for further understanding of the pathophysiological mechanisms linking sleep disturbances during childhood to hormonal abnormalities contributing to the development of obesity and other metabolic disorders. There may be a causal link between sleep loss and weight gain, supported by three hypotheses: reduced activity, REM curtailment, and endocrine disruption, the broad aim of this proposal is to examine the hormonal and metabolic consequences associated with a habitual napping pattern (>3 days per week) into and beyond kindergarten. The proposed study uses a mixed model design where group differences will be assessed over three time points: before kindergarten, immediately after kindergarten, and after transition to kindergarten. Currently, it is unknown whether it is adaptive or not to have a daily napping pattern into school years. Typically, kindergarteners have to adjust their sleep-wake schedules to accommodate for earlier start times (in comparison to preschool) and elimination or curtailment of their nap time. Napping children have a later sleep phase, as evidenced by later bedtimes, more difficulty with sleep onset, and later rise times. Therefore, the start of kindergarten may be particularly difficult for napping children because they may experience sleep loss or circadian dysfunction. As a result of these factors, napping children may experience changes in hypothalamic pituitary adrenal axis functioning, as evidenced by elevated awakening cortisol response (ACR), decreased morning appetite, and an increase in overall calories consumed. The questions addressed in this proposal are (1) will napping into and beyond kindergarten affect sleep distribution differently for habitually napping and non-napping children, (2) will there be a difference in the ACR between habitually napping and non-napping children before and after they transition to a no-nap kindergarten, and (3) will there be a change in morning and daily dietary intake between habitually napping and non-napping children before and after they transition to a no-nap kindergarten that is associated with a change in the ACR. Understanding the causal link between sleep and obesity could lead to treatment/preventative interventions for obesity during childhood.